1. Field of the Invention
The present invention relates to improvements on an accessory which is connected to a control apparatus having control means, such as a microcomputer, a control apparatus to which the accessory is connected, a camera accessory, and a camera to which the camera accessory is connected.
2. Description of Related Art
Heretofore, there have been a variety of systems each of which is composed of a combination of an apparatus having a control circuit, such as a microcomputer, and an accessory having no control circuit, such as a microcomputer. For example, one of such systems is a camera system composed of a combination of a camera and a photo-taking lens which is mounted on the camera (the photo-taking lens being supposed to be the old type having no control circuit, such as a microcomputer), or a camera system composed of a combination of a photo-taking lens and a telephoto converter which is mounted between the photo-taking lens and a camera body to change the photo-taking magnification (or an extender, such as an intermediate ring, used for close-up photo-taking).
In such a system, when the accessory is connected to the apparatus, it is necessary to detect what kind of accessory it is, in order to enable a control operation of the apparatus with the accessory connected thereto. An example of a circuit arrangement for detecting the kind of accessory connected to the apparatus is shown in FIG. 26.
In FIG. 26, reference numeral 101 denotes an apparatus having a control circuit, such as a microcomputer, reference numeral 102 denotes the control circuit, such as a microcomputer, reference numeral 103 denotes a controlled circuit which is to be controlled by the control circuit 102, and reference numeral 104 denotes a battery serving as a power supply. Reference numeral 105 denotes an accessory which is connected to the apparatus 101. The apparatus 101 and the accessory 105 are connected to each other at two terminals EXT0 and COM.
FIG. 27 is a circuit diagram showing the details of the control circuit 102. In FIG. 27, reference numeral 106 denotes a control part of the control circuit 102, and reference numerals 107, 108, 109 and 110 denote diodes for protecting the terminals EXT0 and COM. Reference numeral 111 denotes a resistor connected to a power supply VDD to pull up the terminal EXT0, and reference numeral 112 denotes an input circuit. Reference numeral 113 denotes an N-channel FET (field-effect transistor) arranged to connect the terminal COM to the ground GND. Reference numeral 114 denotes a connection line for connecting the control part 106 to another circuit, and reference numerals 105x and 105y denote two kinds of the accessory 105, which are usable with the apparatus 101.
In the above-described construction, when the accessory 105x is connected to the apparatus 101, since two terminals of the accessory 105x are in no short-circuited relation, an input voltage Vin of the input circuit 112 is pulled up by the pull-up resistor 111, so that the logic of the input voltage Vin of the input circuit 112 becomes xe2x80x9c1xe2x80x9d. On the other hand, when the accessory 105y is connected to the apparatus 101, since two terminals of the accessory 105y are in a short-circuited relation, the terminals COM and EXT0 are short-circuited, so that the logic of the input voltage Vin of the input circuit 112 becomes xe2x80x9c0xe2x80x9d. Thus, the control part 106 is able to know whether the accessory 105 which is now mounted on the apparatus 101 is the accessory 105x or the accessory 105y, according to whether the logic is xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d.
In the above manner, it becomes possible to accurately detect the kind of accessory connected to the apparatus. Accordingly, it becomes possible to appropriately change the operation of the photo-taking lens according to the kind of an extender mounted between the camera body and the photo-taking lens.
In accordance with one aspect of the invention, there is provided an apparatus to which an accessory is connected, the apparatus comprising a plurality of connection terminals at which the accessory is connected, first detection means for detecting states of the plurality of connection terminals by setting at least one connection terminal of the plurality of connection terminals for signal outputting, second detection means for detecting states of the plurality of connection terminals by setting at least one connection terminal of the plurality of connection terminals for signal outputting, the connection terminal set for signal outputting by the second detection means being different from the connection terminal set for signal outputting by the first detection means, and determination means for determining a kind of the accessory mounted to the apparatus, on the basis of results of detection provided by the first detection means and the second detection means. Accordingly, the states of the plurality of terminals are detected twice while changing over the connection terminals set for signal outputting, so that it is possible to increase the number of kinds of accessories which are determinable by the apparatus, without increasing the number of connection terminals of the apparatus.
The above and further aspects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.